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                [Usaco2017 Open]Modern Art                </h1>
                <p>时间限制：10s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：128MB</p>			</div>
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                                <h3>题目描述</h3><p><div>
<div>modeArt critics worldwide have only recently begun to recognize the creative genius behind the great</div>
<div>bovine painter, Picowso.Picowso paints in a very particularway. She starts with an N&times;N blank canvas</div>
<div>, represented by an N&times;N grid of zeros, where a zero indicates an empty cell of the canvas. She then</div>
<div>draws N2 rectangles on the canvas, one in each of N2 colors (conveniently numbered 1&hellip;N2). For examp</div>
<div>le, she might start by painting a rectangle in color 2, giving this intermediate canvas:</div>
<div>2 2 2 0&nbsp;</div>
<div>2 2 2 0&nbsp;</div>
<div>2 2 2 0&nbsp;</div>
<div>0 0 0 0</div>
<div></div>
<div>She might then paint a rectangle in color 7:</div>
<div></div>
<div>2 2 2 0&nbsp;</div>
<div>2 7 7 7&nbsp;</div>
<div>2 7 7 7&nbsp;</div>
<div>0 0 0 0</div>
<div></div>
<div>And then she might paint a small rectangle in color 3:</div>
<div></div>
<div>2 2 3 0&nbsp;</div>
<div>2 7 3 7&nbsp;</div>
<div>2 7 7 7&nbsp;</div>
<div>0 0 0 0</div>
<div>Each rectangle has sides parallel to the edges of the canvas, and a rectangle could be as large as t</div>
<div>he entire canvas or as small as a single cell. Each color from 1&hellip;N^2is used exactly once, although&nbsp;</div>
<div>later colors might completely cover up some of the earlier colors.Given the final state of the canva</div>
<div>s, please count how many of the N^2colors could have possibly been the first to be painted.</div>
<div>
<div>给定一个n*n的矩阵，初始都为0，选择一个1到n*n的排列，然后按照这个排列的顺序，每次选择这个矩阵的一个非</div>
<div>空子矩形，然后涂上当前数字。现在给定最终的矩阵，求哪些数字可能是排列的第一位。</div>
</div>
<div></div>
</div>
<div></div>
<p></p></p><hr/><h3>输入格式</h3><p><div>The first line of input contains N, the size of the canvas (1&le;N&le;1000). The next N lines describe t</div>
<div>he final picture of the canvas, each containing N integers that are in the range 0&hellip;N^2. The input i</div>
<div>s guaranteed to have been drawn as described above, by painting successive rectangles in different c</div>
<div>olors.</div>
<div></div>
<p></p></p><hr/><h3>输出格式</h3><p><div>Please output a count of the number of colors that could have been drawn first.</div>
<div></div>
<p></p></p><hr/><h3>样例输入</h3><pre>4
2 2 3 0
2 7 3 7
2 7 7 7
0 0 0 0</pre><hr/><h3>样例输出</h3><pre>14

In this example, color 2 could have been the first to be painted. Color 3 clearly had to have been p
ainted after color 7, and color 7 clearly had to have been painted after color 2. Since we don't see
 the other colors, we deduce that they also could have been painted first.</pre><hr/><h3>提示</h3><p>没有写明提示</p><hr/><h3>题目来源</h3><p>Platinum </p>
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